As an apparatus for identifying an inertia in the motor control, there is an apparatus proposed in Japanese Patent Application Hei. 8-230713 by the same applicant as the present invention, for example.
This apparatus includes a speed control section for determining a torque command and controlling a motor speed so that an actual motor speed coincides with an inputted speed command, an estimation section for simulating the speed control section so that a speed of a model coincides with the motor speed, and an identifying section for identifying an inertia on the basis of a ratio between a value which is obtained by time-integrating a speed deviation of the speed control section during a specified period and a value which is obtained by time-integrating a speed deviation of the estimation section during the same period. When the speed deviation of the estimation section is zero and the motor speed is not zero during the specified period, the identifying section performs the calculation for identifying the inertia by using the ratio between the value obtained by time-integrating the speed deviation of the speed control section and the value obtained by time-integrating the speed deviation of the estimation section. In contrast, when the speed command and the motor speed of the speed control section are zero, the time integration within the identifying section is not performed. This apparatus performs the identifying operation on real-time as to an arbitrary speed command, so that the identification of the inertia can be performed even if the inertia changes every moment.
As another method for adjusting an inertia in the motor control, there is a control apparatus for a motor servo system disclosed in Japanese Patent Unexamined Laid-open No. Hei. 4-325886. The publication discloses the control apparatus for a motor servo system which feedback-controls a controllable subject formed by a motor and a mechanical system coupled to the motor. Further, the publication discloses that, since a magnitude of a load inertia is directly reflected on a time-integration value of the current flowing into the motor, time-integration values of the current detection values at an actual servo system and a simulation section thereof in the case of adding the same positional command values are obtained, then a magnitude of the load inertia of the controllable subject is identified while modifying a supposing value of the inertia in accordance with the result of the comparison between the time-integration values, then the control gain within the feedback control loop is adjusted on the basis of the identified value of the load inertia, so that the most suitable operation can be easily realized even if the load inertia changes.
However, in this prior art, the inertia can not be identified in the case where the integration value of the speed deviation within the speed control section or the integration value of the speed deviation within the estimation section becomes zero depending on the integration period for time-integrating the inputted speed command or the speed deviation.
Further, in the case where there are friction and disturbance, since a friction compensation component and a disturbance compensation component are contained in the torque command or the motor current in addition to a command response component, it is required to eliminate the influence due to such compensation components. Further, since it is difficult to coincide the actual speed with the speed of a model depending on the inertia, the trial and the calculation for identifying the inertia is required to be performed several times, so that it takes much time for identifying the inertia. As a result, it has been difficult to perform the tuning on real-time with high accuracy.